Research On Single Phase To Ground Fault Line Selection Of Small Current Grounding System

In China,the medium and low voltage distribution networks are mostly operated by small current grounding.The small current grounding system is mainly divided into neutral ungrounded,arc suppression coil grounded and resistance grounded systems.After continuous trial and error,at present,the first two systems are mainly used in the distribution network of our country.The single-phase ground fault has the largest probability,accounting for more than 80%.When the fault occurs,the fault information is interfered by many kinds of external factors,resulting in small fault current and complex fault situation.As a result,the trouble of fault line selection is caused.Therefore,it is very important to study a universal line selection method.The method of fault line selection only depends on a certain characteristic difference between normal line and fault line is no longer universal.Therefore,this paper proposes a new method of fault line selection for small current single-phase ground fault based on fuzzy fusion from the point of view of mutation,energy and polarity of zero sequence current before and after fault.In this paper,firstly,two kinds of widely used small current grounding systems in China are analyzed theoretically,and the normal operation of the two systems and the changes of electrical quantities after faults are understood;secondly,the simulation model of small current grounding system is built by using Simulink,and the correctness of the model is verified by comparing the simulation results and theory,thus the more reliable fault data is obtained;secondly,the original data is extracted The transient information in the initial fault data is preprocessed by wavelet transform,and the effective fault data after preprocessing is processed and selected by modulus maximum method,zero sequence energy method and polarity method respectively,which verifies the feasibility of each method.Finally,the decision-making of the three methods is synthesized by fuzzy information fusion,and the output y with high reliability is obtained,the larger the value of Y,the more likely the obstacle is,selects the line accordingly.In order to verify the feasibility and universality of the algorithm,this paper first simulates different fault conditions by adjusting the model parameters,so as to obtain a large number of fault data and test the algorithm with the data;Secondly,the fault simulation circuit of ungrounded system is built in the laboratory environment,and the algorithm is tested by collecting the actual fault data.Finally,combining the two test results,we can draw the following conclusions:the algorithm in this paper gives full play to the advantages of modulus maximum method,zero sequence energy method and polarity method,and can identify bus fault and feeder fault at the same time,and the method is not affected by fault distance,fault initial angle,transition resistance,noise and grounding mode,and can correctly select the line,especially in high resistance grounding and small grounding In the case of fault angle grounding and long-distance grounding,the fault line can also be correctly identified,which verifies the applicability of the method,and improves the accuracy of line selection compared with the single line selection method.